As described in Japanese Patent Application Laid-Open Nos. 2002-310943, 2014-134528, and 2006-242611 and Japanese Translation of PCT Patent Application Publication No. 2010-523950 (hereinafter called Patent Literatures 1 to 4, respectively), three-dimensional measurement X-ray CT apparatuses, which obtain tomographic images of objects in nondestructive manner, are known. As shown in FIGS. 1A and 1B, such a general three-dimensional measurement X-ray CT apparatus includes an X-ray tube (X-ray source 12) for producing X-rays, a rotary table 16 for rotating an object 10 mounted thereon, and an X-ray detector 14 for detecting the X-rays to capture radiographic images of the object 10. The three-dimensional measurement X-ray CT apparatus performs a CT scan in which while the rotary table 16 rotates the object 10, the X-ray source 12 emits the X-rays, and the X-ray detector 14 detects the X-rays to capture the radiographic images of the object 10. The radiographic images are reconstructed to produce a tomographic image of the object 10.
To obtain the tomographic image of the object 10, the CT scan and the image reconstruction are performed. In the CT scan, the object 10 situated on the rotary table 16 is rotated continuously at a constant speed or intermittently at a constant step width, while being irradiated with the X-rays, so that the radiographic images of the object 10 are captured in an entire circumferential direction. The radiographic images of the object 10 captured in the entire circumferential direction are reconstructed into the tomographic image of the object 10 using a reconstruction algorithm such as a back projection method and a successive approximation method.
To obtain a high resolution tomographic image of the object 10 having short sampling intervals, the object 10 during the rotation is required to be projected largely onto the X-ray detector 14 in the CT scan. Thus, in general, as shown in FIG. 2, the object 10 is situated at the rotation center of the rotary table 16, and the rotary table 16 is brought near the X-ray source 12 along an X axis to scale up the radiographic images. In this situation, the object 10 has to be manually repositioned whenever changing a region of interest, unless a specific unit is provided to adjust the position of the object 10.
However, the rotary table 16, together with the X-ray source 12 and the X-ray detector 14, is installed in an X-ray shield room that shields the X-rays. The repositioning of the object 10 requires much time and effort, owing to operations for X-ray emission control to prevent X-ray exposure of an operator, interlock control to open and lock the X-ray shield room, and the like, thus deteriorating operation efficiency. The same goes in situations that obtain a partially enlarged tomographic image of the object 10. A region of interest of the object 10 is required to be positioned at the center of the rotary table 16.
Note that, some of the three-dimensional measurement X-ray CT apparatuses have an XY shift mechanism on the rotary table to adjust the position of the object, as described in Patent Literatures 1 and 2.
However, the provision of the XY shift mechanism complicates the structure of the apparatus, and increases manufacturing costs.
Patent Literatures 3 and 4 describe the provision of an XY shift mechanism under the rotary table, but do not conceive of a rotation center set at an arbitrary position on the rotary table, as in the present invention.